Contact materials



Feb. 27, 1945. H. GRAVES, JR

CONTACT MATERIAL Filed Sept. 25, 1941 v M NTOR; BY Was/:01 C ill rx W Ma m PatentedjFeb',

uNiTEo? STATES PATENT entice} 1 m .1 C. Pai, asrinor to I. '1. E.Circuit Breaker Company, Philadelphla,-Pa., a corporation ofPennsylvania A plication September 25. 1941. Serial No, 412,215 a;"4asims. (onto-ice) v My invention relates to an electrical contactthemass'are defined by the intersprsedand subcircuitmaking and breakingelement and more particularly to a-combination copper and cadmiummaterial tor forming the same.

of another contact element in order to provide a currentpaththerehetween.

The contact it comprises a or copper t2, the pores of-whichare howeverir'aii, filled wlthfcadmium E3, in a pure or relatively pure state. Themass of copper i2 is substantially laminar in composition with each ofthe ltions exrelatively porous the two materials are soluble estantially continuous cadmium particles; "which 1 s are either in a pureor partially alloyed form. l Since the contact I 0 is manufactured y by'a It is well hnownth'at copberand alloy in such a manner that neither.el be disuished microscopi" can other It this were the case. in a setofcontacts.- none, of the advantages, hereinafter set forth, obtained bythe useoi iree cadmium would be achieved.

It is necessa y tor the correct? operation or the contact that ireecadmium belpresent near the.

mm, in a plane substantia y nareuei to tha 55 earth: the contact, n 9Prevent of the face M or the contact. The an i "1 hthr words, I

Heretofore, various types of contacts have'been .5 sintering operationfrom particles of copper{ and proposed and used in an attempt to lowerconcadmium which, are compressed and"c'aused-to tact resistance,increase the wearing qualities, flow lnto'laminar form, each ofthelaminations f H and decrease welding. Thus, contacts made or a of thecopper l2 iS'Of minutethickness, and silver graphite combination,or ofcadmium plated "w aring or flak ng fl of Surf ce laminations copper 'orsilver, or even of a copper and cadlib when the contact is in u ecausesno appretlablfl mium allo have been used. wear. v v

But, an object of this inventionis the utiliza- I must be emph sizedthat the drawlns oi. tion 01 cadmium in a free state or relatively freeFigure 2 erely schematic. The laminatiohs state in th contact, K of thefinished copper need not be as regular or A further object of thisinvention is the forw W ll defined as in the drawing.v And the eadmationof a contact material or a substantially mium particles neednot-necessarily be in the laminar structure having particles or anotherform of flakes of minute thickness but may be material dispersed betweenthe laminations. f ar o flas le e fo w e, nevertheless Another objectorthis invention is the formae g the laminations of the finished tion of acontact of substantially laminar st'rucso The specific operations bywhich the contact ture with particles of an additional material t l mufee ured wi l behereinafter described. having a lower melting pointthan the principal Iheve found t there is a wide euse of material ofthe-contact dispersed between the t ns under wh h the c pper cadmiumlaminations, contact of my invention will have y' advan- Still furtherobjects of this invention include td't e s pp r or silver: the formationof a, contact having low contact Whemthe t-c nsists Of a bodyoi pu eresistance, no tendency to weld, high conductiv "copper fil d with pureum.. ity, strength and resistance to physical shock and Where thecontact consists of an al v of abrasion, high resistance to erosion, andoflow copper and cadmium fil i fp e admium. t V 3. ere thecontact-consists of pure copper These and many other objects of thisinvenfi led with an alloy of 0996 ndmdmium. tion will in part beapparent and, where not l' t consists copper a apparent, pointed out, inthe following descrip 111mm alloy high in pp fi ed w th an alloy .tionand drawing in which: of pe and admium in um. v

Figure 1 is a side view of a contact formed from 35 l f h eg i s e am rtr my novel mp a ture of the type above described has been found Figure2 is a schematic fragmentary cross-secw be wmnmgwusi mwever' the m i istional view of a minute portion of a corner of the i we PD I even thoughthis 1 contact of Figure 1. gg is not P t A Referring now to Figures 1and 2, Ihave here an fadmtage a maftgiial 9 shown inschematic form, acontact member 86' $53 s 1 g;

, constructed in accordance with my invention. tends to educ 5 i L 3%The face ii of the contact member is intended, assisting Sn outing-am e.7 3 during operatiomtc be in contactwith-the face 5 M m the contactsunder arcing conditions and to decrease milli-volt drop. Otherwise, ifan alloy is used, a quantity of copper must be volatilized before anycadmium is set free.

As a result of the relatively low boiling point of pure cadmium and alsothe low ionization temperature, a contact made thereof will tend tomaintain the arc stream at a relatively low temperature. However,cadmium cannot be used alone owing to the high temperatures presentduring the arc. The advantages of the use of cadmium may however beobtained if a quantity thereof is set free during the drawing of thearc.

During engagement, the circuit breaker contacts provide low resistancecausing a normal temperature rise. Upon the occurrence of a fault, theincreased current will generate heat which is a product of the square ofthe current value and the resistance. Moreover, the resistance betweenthe contacts increases rapidly and the heat generated further increasescorrespondingly.

The are is drawn at a single point on the contact. The temperature ofthis point is extremely high, above the vaporizing point of any contactmaterial. Heat radiates from this point through a hemisphere ofmaterial, the temperature gradient depending upon the thermalconductivity of the contact material. Consequently, there are surfacetemperature zones of metal in different conditions: solid, plastic,molten, vaporizing. Under these conditions, contacts composed of puremetals or alloys are very apt to weld or stick together.

When, however, there exists (as in the case of the present contact)directly behind an area of plastic material, a film or layer of material(such as cadmium) that, at the same temperature or even at aconsiderably lower temperature, is in a vaporizable or molten state,then the force pushing the contacts apart will be able to pull off metalflakes within the plastic area and free the contacts. This is moreparticularly true when the contact structure is a laminar one as abovedescribed.- Local explosions of the highly volatile material may occurat the points of high current density corresponding to points of flnalcontact separation and assist the flaking process.

Contacts of this type thus tend to shed flakes of metal upon each otherduring heavy current interruption. Due to the fine grain structureemployed, this produces relatively little roughness on the surface.Chemical analysis indicates that this process has a tendency to reducevery slightly the percentage of the secondary material. Theeffectiveness of the contacts is not, however, altered.

The explosive action of the cadmium has a As soon as the cadmium vaporcomes into contact with air it is oxidized. The oxide is a goodinsulator and will not provide a low resistance path for dielectricbreakdown. This is in contrast to the current path formed along adjacentinsulators by particles of silver or carbon when contacts containin suchmaterials are used.

The cadmium oxide formed on the surface of the contact as a result ofarcing is extremely friable and is easily removed from the surface bythe wiping action of the contacts. This is particularly true when thesurfaces have been slightly roughened by current interruption. The highpoints of the contacts are wiped clean and the oxide may be transferredto the depressions. Since the laminar construction above describedenhances non-welding qualities of my contact, it becomes important toutilize particles for forming the same which are as small and thin aspossible. Since the particles of copper are held together by a solder(cadmium) which melts at a lower temperature, local heating of thecontact permits small areas of copper to flake off, remaining engaged tothe other contact block. The smaller the particles and the thinner theyare, the less the roughness caused at the contact surface by the flakinoff. And, if the particles are in the form of flakes lying in planesparallel to the plane of the contact surface, any roughness causedby theflaking off will be greatly reduced. In one method of manufacture of mycontacts, the thinnest possible flakes of copper (produced in a ballmill and annealed) are plated with cadmium by the standard barrelelectro-plating process and aligned, asfar as possible, in parallelplanes by vibrating the loose mass. The cadmium deposit may beapproximately five to ten percent by weight of the total. The thicknessof the plating film should, however, be suflltendency to blowout the arcand decrease the amount of arcing once the arc is struck. The very lowmelting point and boiling point of cadmium makes possible the evolutionof cadmium vapor at a fairly low temperature. The heat of vaporizationof cadmium is such that it does not require a great deal of energy tovaporize a given .amount of cadmium. The cadmium may be doubly ionizedat fairly low voltages so that the charge on the ions is +2e, where e isthe charge of the electron.- Because of its fairly high atomic weight(112) it willcmove relatively slowly in the are stream.

As a result of these characteristics, cadmium is able to absorbconsiderable energy in the arc without causing undue stress onthe-contacts or on the surrounding materials.

cient to produce the flaking off effect and are snufllng resultspreviously set forth. Additional free cadmium may be added if it isdeemed necessary for particular uses of the contact or electrodes. 1 i IThe mass of plated flakes is then compressed to a substantially solidblock preferably by a pressure of the order of 60,000 pounds per squareinch to eliminate most of the voids in the mass.

The compressed mass is then sintered.

The cadmium plate then forms a homogeneous bond between the copperflakes. The sintered material may then be repressed at a low temperatureto break up the continuous cadmium bond and to cause it to crumble; bywhich means, a grain structure is produced in the' contact which may becaused to be substantially parallel to the plane of the contact face.This latter step is, however, not essential.

It may be difficult, however, to cause the copper flakes to arrangethemselves in substantially parallel relation.

Accordingly, an alternative method comprises the steps of utilizinggrains of copper in a form approximating a sphere, plating them asabove, and compressing them-into flat plates. A cake of the platedgrains is formed and then subjected to pressure as above, allowing theedges of the cake to fiow out. While the flakes thus produced are not asthinas in the case of ball mill flakes, a better alignment is obtained.The previous plating of the copper with cadmium provides a lubricant toassist the. flow. The mass may then be sintered and treated in themanner above described.

In another method, no plating operation is perasrdcco formed, but thefinely divided copper and cadmium are intimately mixed, compressed,sintered and repressed as above set forth. In this process, the cadmium,as it wets the surface of the copper, flows through the copper mass bycapillary action. The bond thus produced may not be as good asthatformed'by the plating method, but provides local areas of cadmium.These lat ter will cause an additional action'during currentinterruption when their temperatures exceed the vaporizing point. Localexplosions may thus occur which will assist in the flaking operation. I

In any of these sintering operations, a small quantity of finely dividedgraphite may be intermixed with the mass to lubricate the particles andto facilitate the flow of metal during compression and sintering and todecrease the tendency to weld during operation. Such graphite particlesare shown schematically at id of Fig. 2.

An analysis of the cadmium copper contact thus formed by any of thesemethods shows a matrix of pure copper interspersed-with a substantiallycontinuous binder of pure cadmium.

The method for forming abontact described above may be extended tovarious materials other than copper as a basic material. Thus it ispossible to employ such refractory materials as tungsten or molybdenumand form a contact of such material combined with a low boiling pointmetal such as cadmium. Similarly materials such as silver, nickel, iron,

cobalt, gold, platinum or palladium may be employed to replace thecopper used as the basic material in my-contact; and, further, thecadmium itself may be replaced by other metals of low boiling pointwhichassist in snufiing an arc.

Thus it may be seen that I may employ various granulatedmetals incombination and by a process including the steps of compression,sintering and recompres sion, form a contact having a laminatedconstruction which isdesirable for circuit interrupters in high currentcircuits. Furthermore, if one of the finely divided metals employed is ametal of low boiling point, the

arc extinguishing properties of the circuit inter-- rupter are enhancedby the contact itself.

Hence many modifications of my contact and the means for fabricating thesame will be obvious to those skilled in the metal arts. Thus I preferto be bound not by the specific disclosures herein but only by theappended claims.

I claim:

1. An electrical contact having a surface for engaging a second contact,said contact compris ing a quantity of finely divided conducting copper,a quantity of a second finely divided conducting material of a lowermelting point, said materials being compressed and sintered together ina compact mass, a pluralitytcf the particles of said first materialbeing in the form of flakes extending in planes approximately parallelto said surface.

2, An electrical contact having a surface for engaging a second contact,said contact comprising a quantity of finely divided conductingmaterial, ,a quantity of a second finely dividednconducting puremetallic badmium of a. lower melting point and a quantity of finelydivided carbon, said materials being compressed and sintereitogether ina compact mass, a plurality of the particles of said first materialbeing in the form of flakes extending in planes approximately parallelto said surface. i

3. An electrical contact having a surface for engaging a second contact,said contact comprising a quantity of finely divided metal of highelectrical conductivity, a quantity of finely divided metallic cadmium,said materials being compressed and sintered together in a compact mass,the particles (if said metal of high conductivity being predominantly inthe form of flakes extending in planes parallel to .the surface.-

An electrical contact comprising a quantity of finely divided copper inthe form of elongated particles extending in planes substantiallyparallel to the surface of the contactand a quantity of a second finelydivided metallic conducting.

material of a lower melting point than cbpper, said materials beingcompressed and sintered together in a compact mass. 1

' HERBERT C. GRAVES, JR.

